Bacterial endotoxin has been found to inhibit the synthesis of hepatic tryptophan oxygenase and phosphoenol pyruvate carboxykinase induced by glucocorticoid injections in mice. The nature of his action is known and its elucidation is the objective of the proposed work. Up to the present time, attempts to identify the source of a mediator released by target cells in response to an injection of endotoxin have yielded inconclusive results. Continued effort should clarify the reality of the postulated mediator. As these experiments proceed, a hepatoma cell line from rats, in which one or both of the above enzymes can be induced by the addition of glucocorticoid to the medium, will be used to determine whether the presence of endotoxin has an effect similar to that seen in mice. If endotoxin acts directly on enzyme induction or requires the presence of target cells, can be determined and then the nature of its action should be more easily resolved than is now possible.